JP2023067830A - Gas-barrier sheet - Google Patents

Abstract

To provide a gas-barrier sheet having excellent gas barrier property as well as practical utility.SOLUTION: Disclosed is a pulp fiber having one kind selected from a group consisting of a general formula (1), a general formula (2), and a general formula (3) in at least a part of a constitutional unit of cellulose. An introduction amount of SO3-Z in a case of having the general formula (1), an introduction amount of CO2-Z in a case of having the general formula (2), and an introduction amount of PO3-Z in a case of having the a general formula (3) are 0.8 mmol/g or over and 5 mmol/g or under, and an oxygen permeation degree measured by JIS K 7126-1 (differential pressure method) is 200 (cc/m2 24 hour atm) or under. Therefore, a sheet having gas barrier property with improved practical utility can be provided.SELECTED DRAWING: Figure 1

Description

The present invention relates to gas barrier sheets. More particularly, it relates to a gas barrier sheet having gas barrier properties.

Since paper is produced from wood pulp, which is a plant-derived natural material, which is one of the renewable resources, paper is attracting attention as a plastic-free alternative material from the viewpoint of recent sustainable development goals.
Paper generally has a thickness of several hundred μm. Processing such as lamination of films or the like is performed.
2. Description of the Related Art Conventionally, packaging materials used for packaging foods, pharmaceuticals, electronic components, and the like use sheets with low oxygen permeability (gas barrier sheets) in order to prevent oxidation and deterioration of contents. Materials for such gas barrier sheets are mainly resin films and cellophane, but in recent years, techniques using cellulose nanofibers have been developed (for example, Patent Documents 1 and 2).
Patent Documents 1, 2, and 3 disclose sheets containing cellulose nanofibers, and describe that such sheets have gas barrier properties.

Japanese Patent Publication No. 2011-40547 Japanese Patent Application Publication No. 2011-118520 Japanese Patent Application Laid-Open No. 2020-073706

However, since the sheet of the above document contains cellulose nanofibers, the gas barrier properties of the sheet are remarkably deteriorated due to bending and the like, and the fact is that the sheet has not yet been put to practical use.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas barrier sheet that has excellent gas barrier properties and can withstand practical use.

As a result of earnest studies to solve the above problems, the present inventor found that the above problems can be solved, and completed the present invention.

The gas barrier sheet of the present invention is a paper sheet member containing chemically modified pulp fibers in which a predetermined anionic substituent is introduced into some of the cellulose structural units, and the sheet obtained from the chemically modified pulp fibers is It is characterized by exhibiting an oxygen permeability of 200 or less.

Although the gas barrier sheet of the present invention is made of paper, it has a structure capable of exhibiting gas barrier properties by containing chemically modified pulp fibers having an oxygen permeability of a predetermined value or less. Moreover, since it is made of paper, its flexibility is maintained. Therefore, it is possible to provide a sheet having gas barrier properties with improved practicability.

1 is a schematic flow diagram of a method for manufacturing a gas barrier sheet of the present embodiment; FIG. It is the figure which showed an example of an experiment result. It is the figure which showed an example of an experiment result. It is the figure which showed an example of an experiment result.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described based on the drawings.
The gas barrier sheet of the present embodiment is a paper sheet containing chemically modified pulp fibers having predetermined anionic substituents in some of the cellulose constitutional units, but is capable of imparting excellent gas barrier properties. It is characterized by

The outline of the structure of the gas barrier sheet of this embodiment will be described.
The gas barrier sheet of this embodiment is a sheet-like member containing predetermined chemically modified pulp fibers.

First, an outline of the chemically modified pulp fibers contained in the gas barrier sheet of the present embodiment (hereinafter simply referred to as the chemically modified pulp fibers of the present embodiment) will be described. The chemically modified pulp fiber of the present embodiment is a pulp fiber having a predetermined anionic substituent on a part of the cellulose constitutional units.
Specifically, cellulose (also referred to as a cellulose molecule) is a chain of D-glucose represented by the following general formula (1) (where m is an integer) β (1 → 4) glycosidic bonds It is a polymer. Pulp fibers are aggregates of multiple celluloses. Details will be described later.
This chemically modified pulp fiber is a pulp fiber obtained by introducing predetermined anionic substituents (SO ₃ ⁻ Z, CO ₂ ⁻ Z, PO ₃ ^{2 −} Z) into cellulose as described above. That is, this chemically modified pulp fiber has at least one structure selected from the group consisting of the following general formula (2), general formula (3) and general formula (4) in at least part of the cellulose constitutional units. It is a pulp fiber manufactured in

(general formula (1))

（式中、Ｒ_１は、ＳＯ_３ ^－Ｚ又はＨを示す。ただし、Ｒ_１は、同一でも異なっていてもよい。またＳＯ_３ ^－Ｚを少なくとも１以上含む。Ｚは、水素イオン、金属イオン、オニウムイオンまたはカチオン性有機化合物を示す。ｎは１以上の整数を示す。） (general formula (2))

(In the formula, R ₁ represents SO ₃ ⁻ Z or H. However, R ₁ may be the same or different, and contains at least one SO ₃ ⁻ Z. Z is hydrogen ion, metal ion , represents an onium ion or a cationic organic compound. n represents an integer of 1 or more.)

A maximum of three SO ₃ ^-Z can be bound to D-glucose of cellulose. Therefore, Z is selected from the group consisting of hydrogen ions, alkali metal cations, monovalent transition metal ions, onium ions (ammonium ions, aliphatic ammonium ions, aromatic ammonium ions, etc.), and cationic polymers. It can be at least one. In some cases, Z is at least one selected from the group consisting of compounds containing two or more cationic functional groups in the molecule, such as alkaline earth metal cations, polyvalent metal cations, and diamines. .

（式中、Ｒ_２は、ＣＯ_２ ^－Ｚ又はＨを示す。ただし、Ｒ_２は、同一でも異なっていてもよい。またＣＯ_２ ^－Ｚを少なくとも１以上含む。Ｚは、水素イオン、金属イオン、オニウムイオンまたはカチオン性有機化合物を示す。ｎは１以上の整数を示す。） (general formula (3))

(In the formula, R ₂ represents CO ₂ ⁻ Z or H. However, R ₂ may be the same or different, and contains at least one CO ₂ ⁻ Z. Z is hydrogen ion, metal ion , represents an onium ion or a cationic organic compound. n represents an integer of 1 or more.)

Note that CO ₂ ⁻ Z can bind to D-glucose of cellulose up to three. Therefore, Z is selected from the group consisting of hydrogen ions, alkali metal cations, monovalent transition metal ions, onium ions (ammonium ions, aliphatic ammonium ions, aromatic ammonium ions, etc.), and cationic polymers. It can be at least one. In some cases, Z is at least one selected from the group consisting of compounds containing two or more cationic functional groups in the molecule, such as alkaline earth metal cations, polyvalent metal cations, and diamines. .

（式中、Ｒ_３は、ＰＯ_３ ^2－Ｚ又はＨを示す。ただし、Ｒ_３は、同一でも異なっていてもよい。またＰＯ_３ ^2－Ｚを少なくとも１以上含む。Ｚは、水素イオン、金属イオン、オニウムイオンまたはカチオン性有機化合物を示す。ｎは１以上の整数を示す。） (general formula (4))

(In the formula, R ₃ represents PO ₃ ^2- Z or H. However, R ₃ may be the same or different, and contains at least one PO ₃ ^2- Z. Z is a hydrogen ion, represents a metal ion, an onium ion, or a cationic organic compound, where n represents an integer of 1 or greater.)

Note that PO ₃ ^2- Z can bind to D-glucose of cellulose up to three. Therefore, Z is selected from the group consisting of hydrogen ions, alkali metal cations, monovalent transition metal ions, onium ions (ammonium ions, aliphatic ammonium ions, aromatic ammonium ions, etc.), and cationic polymers. It can be at least one. In some cases, Z is at least one selected from the group consisting of compounds containing two or more cationic functional groups in the molecule, such as alkaline earth metal cations, polyvalent metal cations, and diamines. .

Note that n in formulas (2), (3), and (4) is an integer of 1 or more. n in the formula is appropriately adjusted according to the amount of the anionic substituent introduced into the cellulose. For example, when the polymerization degree of cellulose constituting the chemically modified pulp fiber is 3000, n is 60 or more, preferably 300 or more, more preferably 600 or more.

Further, the anionic substituents (SO ₃ ⁻ Z, CO ₂ ⁻ Z, PO ₃ ²⁻ Z) of the chemically modified pulp fiber of the present embodiment are, for example, 0.8 mmol/g or more and 7 mmol/g or less. . This value is preferably 0.8 mmol/g or more and 5 mmol/g or less, more preferably 0.8 mmol/g or more and 2.5 mmol/g or less, and still more preferably 0.8 mmol/g or more and 2.0 mmol/g. g or less. That is, the introduction amount of SO ₃ ^- Z when having the general formula (1), the introduction amount of CO ₂ ^- Z when having the general formula (2), and the introduction amount of PO ₃ ² when having the general formula (3) ^- The amount of Z introduced is within the range of 0.8 mmol/g or more and 5 mmol/g or less.
The introduction amount of the substituent can be calculated by the method described in the embodiments or examples.

Since the gas barrier sheet of the present embodiment contains the above-described chemically modified pulp fibers, the chemically modified pulp fibers are crushed into a flat plate and laminated in a flat structure (flat plate laminated structure) during production. ing.
Since the gas barrier sheet of the present embodiment has a structure in which chemically modified pulp fibers are laminated while being crushed into a flat plate, the plurality of openings formed on the surface are formed to be extremely small in size. ing. Specifically, the gas barrier sheet of the present embodiment has a plurality of openings formed on the sheet surface in the same manner as general paper (paper formed by intertwining pulp fibers). The openings formed on the surface are gaps formed between the chemically modified pulp fibers crushed into flat plates or between the chemically modified pulp fibers and other pulp fibers. For this reason, the openings formed on the surface of the gas barrier sheet of this embodiment are formed to be much smaller than the openings formed on the surface of general paper. A plurality of fine pores are formed in a mesh-like manner from the opening toward the inside. In other words, the mesh-like pores function as channels (gas channels) through which the gas entering from the sheet surface passes.
Therefore, on the sheet surface of the gas barrier sheet of the present embodiment, the openings of the gas flow paths (gas flow paths) are formed so as to be much smaller than those of general paper.

As described above, the gas barrier sheet of the present embodiment is in a state in which gas is less likely to penetrate than ordinary paper. In addition, in the gas barrier sheet of the present embodiment, since the cross-sectional structure is a structure in which chemically modified pulp fibers having a flat plate shape are laminated, the flow path length of the gas flow path is much longer than that of general paper. formed to be long.
Then, since the length of the gas flow path is formed to be much longer than that of general paper, the flow velocity of the gas entering the gas flow path from the surface can be reduced.
Therefore, the gas barrier sheet of the present embodiment can exhibit excellent gas barrier properties even though it is a sheet made of paper. Moreover, since the gas barrier sheet of the present embodiment does not actively add or generate fine fibers such as cellulose nanofibers, the flexibility of the pulp is maintained.
Therefore, it can be said that the gas barrier sheet of the present embodiment is a highly practical sheet that can exhibit excellent flexibility while exhibiting excellent gas barrier properties, even though it is made of paper.

The gas barrier sheet of this embodiment has a structure that exhibits gas barrier properties, and the structure is based on the chemically modified pulp fibers of this embodiment that it contains. And this gas barrier property can be evaluated by the oxygen permeability of the chemically modified pulp fiber of the present embodiment.
Specifically, the chemically modified pulp fiber of the present embodiment has an oxygen permeability of 200 or less when formed into a sheet. This value is preferably 100 or less, more preferably 50 or less.
The oxygen permeability is the oxygen permeability (cc/m ² ·24 hours·atm) measured according to JIS K 7126-1 (differential pressure method). That is, the sheet obtained from the chemically modified pulp fiber (hereinafter referred to as the test sheet) exhibits a value within the above range as measured according to JIS K 7126-1 (differential pressure method).

Moreover, it is desirable that the gas barrier property is maintained even after the sheet is creased. Specifically, the gas barrier retention property can be evaluated by measuring the above-mentioned oxygen permeability after making a cross crease (bending test).
The oxygen permeability after the bending test of the test sheet of the chemically modified pulp fiber of the present embodiment is 400 or less. It is preferably 200 or less, more preferably 100 or less, and still more preferably 50 or less.

The above test sheet is not particularly limited as long as it is within the range based on the applicable law. This test sheet corresponds to the sheet obtained from the chemically modified pulp fibers in the claims.

For example, the test sheet has a basis weight of 10 g/m ² or more and 150 g/m ² or less. The basis weight is preferably 20 g/m ² or more and 120 g/m ² or less, more preferably 25 g/m ² or more and 115 g/m ² or less.

The thickness (μm) of the test sheet is, for example, 20 μm or more and 150 μm or less. It is preferably 20 μm or more and 140 μm or less, more preferably 30 μm or more and 130 μm or less.

The density (g/cm ³ ) of the test sheet is, for example, 0.3 g/cm ³ or more and 1.5 g/cm ³ or less. It is preferably 0.4 g/cm ³ or more and 1.5 g/cm ³ or less, more preferably 0.4 g/cm ³ or more and 1.2 g/cm ³ or less.

The moisture content of the test sheet is not particularly limited, but is, for example, 20% or less. It is preferably 15% or less, more preferably 10% or less. This moisture content can be measured using an infrared moisture meter (for example, Kett Scientific Laboratory Co., model number: FD-720).

The chemically modified pulp fibers of the present embodiment are preferably formed so that the short fiber rate is equal to or less than a predetermined value. For example, the short fiber rate of chemically modified pulp fibers is adjusted to 2.0% or more. This value is preferably 3.0% or more, more preferably 5.0% or more.
A short fiber indicates a fiber having a fiber length of 0.04 mm or more and 0.2 mm or less. A method for measuring the short fiber rate and the like will be described later.

The gas barrier sheet of the present embodiment is prepared so that the chemically modified pulp fiber accounts for 50% by mass to 100% by mass with respect to the entire sheet. This content is more preferably 80% to 100% by mass, more preferably 90% to 100% by mass.
That is, for example, the gas barrier sheet of the present embodiment, which is formed only from a slurry of chemically modified pulp fibers, is a sheet adjusted so that the chemically modified pulp fibers are 100% by mass with respect to the entire sheet. .

(Manufacturing method of the gas barrier sheet of the present embodiment)
The gas barrier sheet of the present embodiment can be produced by supplying chemically modified pulp fibers prepared to have predetermined properties to a paper machine or the like. Other processes are not particularly limited as long as the paper machine or the like has a pressing process (pressing process). For this pressing step, commonly used methods such as a method of pressing a sheet-like material with a rotating roller, a method of pressing with a press machine, or the like can be used.

For example, the gas barrier sheet of the present embodiment can be produced using a commonly used paper machine having a pressing step that enables pressing in the form of a sheet. The resulting gas barrier sheet has a structure in which the chemically modified pulp fibers are laminated in a state of being crushed (flat state) by the pressing process.
The gas barrier sheet of the present embodiment can be prepared by preparing a pulp slurry in which chemically modified pulp fibers are dispersed and hand-made, as long as it has the above-described pressing step. It can be applied to a substrate, dried and then peeled off, or simply air-dried or heat-dried to form a sheet. For example, if the existing equipment has a process having the same function as the pressing process described above, there is no need to install a special device or the like for manufacturing the gas barrier sheet, which is economically advantageous. . In other words, manufacturing costs can be significantly cut.

The gas barrier sheet of the present embodiment is not particularly limited as long as it is a sheet-like member containing chemically modified pulp fibers in the above range as described above.
For example, the gas barrier sheet of the present embodiment may be a sheet formed only from chemically modified pulp fibers or a sheet formed from fibers containing chemically modified pulp fibers and other pulp or the like. It may be a configuration.

For example, the gas barrier sheet of the present embodiment can employ a structure in which pulp slurry in which chemically modified pulp fibers are dispersed in water is coated on a substrate. That is, the gas barrier sheet of the present embodiment can have a structure having a substrate and a modified pulp layer containing chemically modified pulp fibers. The material of the substrate is not particularly limited, but paper is preferable from the viewpoint of environmental load, but it is needless to say that the material is not limited to such a material.

Moreover, the gas barrier sheet of the present embodiment is not particularly limited, whether it has a two-layer structure or a multi-layer structure, as long as it has a base material and a modified pulp layer. For example, a structure in which a modified pulp layer is laminated on the surface of the base material, a structure in which modified pulp layers are laminated on both sides of the base material, a structure in which a third layer is provided between the base material and the modified pulp layer, etc. A laminated structure can be employed.

When the gas barrier sheet of the present embodiment has a structure having a base material and a modified pulp layer, for example, a pulp slurry in which chemically modified pulp fibers are dispersed is prepared, and this pulp slurry is applied to the base material surface. It can be manufactured by coating. By adjusting the thickness and coating amount of the modified pulp layer, it is possible to adjust the gas barrier property and flexibility according to the application.
The coating amount is, for example, 0.1 g/m ² or more and 20 g/m ² or less. It is preferably 2 g/m ² or more and 10 g/m ² or less, and more preferably 3 g/m ² or more and 7 g/m ² or less.
The term "coating" refers to the formation of a pulp slurry layer (modified pulp layer) on a substrate, and is a concept that also includes coating. For example, a hand coating method using a general coating machine, bar coater, brush, or the like used for papermaking, or a coating method by spraying can be employed.
Moreover, the density|concentration of the pulp slurry used for coating is not specifically limited. For example, chemically modified pulp fibers adjusted to have a solid content concentration of 0.1 to 10% can be used. In addition, one layer may be applied to the base material, or another layer of pulp slurry may be formed on the surface of another coating layer.

The gas barrier sheet of the present embodiment may contain other pulps, resins, etc. as long as it contains chemically modified pulp fibers as described above. For example, if a polymer resin such as polyvinyl alcohol (PVA) is used as the resin, it is possible to improve flexibility, tensile strength, and the like. Moreover, paper strength (dry paper strength and wet paper strength) can be improved by using a pulp fiber surface modifier such as epichlorohydrin. Furthermore, by containing a resin solution such as an ethylene-vinyl alcohol copolymer as an additive, it is possible to obtain the advantage of being able to exhibit excellent suppression of water vapor permeation.

The flexibility of the gas barrier sheet of this embodiment can be measured by the method described in Examples.
For example, a method such as JIS K 5600-5-1 (mandrel bending test) can be used to evaluate whether bending occurs on the surface of the sheet. The occurrence of bending means that openings of flow paths (gas flow paths) through which gas passes on the surface of the sheet exhibiting gas barrier properties are opened, leading to deterioration of gas barrier properties.

(Method for producing chemically modified pulp fibers contained in the gas barrier sheet of the present embodiment)
A method for producing the chemically modified pulp fibers contained in the gas barrier sheet of the present embodiment (chemically modified pulp fibers of the present embodiment) will be described below.

First, the outline of the method for producing chemically modified pulp fibers of the present embodiment (hereinafter referred to as the present production method) will be described.
This manufacturing method is a method of manufacturing by subjecting a fibrous material containing cellulose (for example, wood pulp) to a predetermined chemical treatment process.
In this chemical treatment step, the supplied fiber raw material is brought into contact with a reaction solution (contact step), and then subjected to a heating reaction (reaction step) to add a predetermined anionic substituent to D-glucose, which is a constituent unit of cellulose. It is to introduce.

As used herein, the fiber raw material refers to a fibrous member containing cellulose molecules, and includes, for example, pulp made from wood or the like. Pulp is a member in which pulp fibers are aggregated (aggregate of pulp fibers), and the pulp fiber means a fibrous member composed of a plurality of cellulose fibers. Cellulose fibers are fibrous members in which a plurality of fine fibers (for example, microfibrils, etc.) are aggregated, and fine fibers are chain-like high chains in which D-glucose is β (1 → 4) glycosidic bonds. It means a member in which a plurality of cellulose molecules (sometimes simply referred to as cellulose) are aggregated.

In this manufacturing method, the fiber raw material may be used as it is, or may be washed before use. The washing method is not particularly limited. For example, by filtering and dehydrating using water on a 200-mesh or 235-mesh sieve, fine fibers and dust can be sieved out, so handleability during production can be improved. In other words, fibers with a size that can be a residue of 200 mesh or 235 mesh are the pulp fibers used in the pre-washing. The details of the fiber raw material will be described later.

Each step of the chemical treatment process will be described below.

(Contact process)
The contacting step in the chemical treatment step is a step of contacting the fiber raw material with a compound necessary for introducing the anionic substituent contained in the reaction solution.
A contact method in the contact step is not particularly limited. For example, the fiber raw material (for example, wood pulp) may be impregnated with the reaction liquid by immersing the fiber raw material in the reaction liquid, the reaction liquid may be applied to the fiber raw material, or the fiber raw material may be coated with the reaction liquid. On the other hand, the above compounds may be directly applied (in the case of using a plurality of compounds, they are applied separately), impregnated, or sprayed. For example, if a method of immersing the fiber raw material in the reaction liquid is employed, an advantage can be obtained in that the fiber raw material and the reaction liquid are easily brought into contact uniformly.

The solvent for the reaction solution is not particularly limited as long as it can dissolve or disperse the above compound.
For example, in addition to water alone (including pure water such as ion-exchanged water and distilled water, as well as tap water, etc.), ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, and protons such as ammonia water polar solvents, acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethylsulfoxide (DMSO), dimethylsulfide (DMS), aprotic polar solvents such as dimethylacetamide (DMA), Non-polar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane can be mentioned, and these may be used alone or in combination of two or more. may

The compound used in the reaction solution is not particularly limited as long as it can introduce a predetermined anionic substituent into cellulose (represented by general formula (1)) as described above.
For example, when it has at least a structural unit represented by the following general formula (2), sulfamic acid can be mentioned, and when it has at least a structural unit represented by the following general formula (3), 2, 2, Mention may be made of the 6,6-tetramethyl-1-piperidinyloxy radical (TEMPO). Moreover, when it has at least a structural unit represented by the following general formula (4), ammonium dihydrogen phosphate can be mentioned.

In this specification, the introduction of an anionic substituent is simply referred to as substitution, and after the reaction, a predetermined anionic substituent is bound to at least a portion of the hydroxyl groups that make up the cellulose through a substitution reaction, an oxidation reaction, or the like. It means the state of
Specifically, one or more SO ₃ ^- Z is introduced into D-glucose, which is a constituent unit of cellulose, or one or more CO ₂ ^- Z is introduced, or PO ₃ ^2- Z. means that at least a part of the structural units of cellulose has at least one D-glucose introduced therein.
For example, a structure in which the hydroxyl group at the 6-position of D-glucose, which is a structural unit of cellulose, is introduced with anionic SO ₃ ⁻ Z or PO ₃ ^2- Z by a substitution reaction (a structure in which the above substituents are so-called ester-bonded structures, such as general Formula (5) and general formula (7)), and a structure in which the hydroxyl group at the 6-position of D-glucose is replaced (substituted) with CO ₂ ^- Z by an oxidation reaction (for example, general formula (6)) can be mentioned. can.

The structure in which the substituent is introduced only at the 6-position of D-glucose includes general formula (5), general formula (6) or general formula (7). It is not limited to these.
For example, as described above, in addition to the structure in which any one of the above substituents is introduced at any of the 2-, 3-, and 6-positions of D-glucose, a structure in which two of these substituents are introduced, A structure in which three are introduced may be used.

(general formula (5))

(general formula (6))

(general formula (7))

In the above example, in at least a part of D-glucose of the structural units of cellulose constituting the chemically modified pulp fiber of the present embodiment, the substituent (SO ₃ ^- Z, CO ₂ ^- Z, or PO ₃ ^2- Z) were introduced, but in addition to the above structures, D-glucose having the above substituents introduced at each carbon position (e.g., -C- SO ₃ ^— Z, —C—CO ₂ ^— Z, —C—PO ₃ ^{2 —} Z) as structural units. As these structures, for example, as described above, in addition to the structure in which any of the above substituents is directly introduced to any one of the carbons at the 2-, 3-, and 6-positions of D-glucose, these introducible positions may be a structure in which two of the above substituents are introduced, or a structure in which three of the above substituents are introduced.

(When the structural unit has the general formula (2))
Hereinafter, the chemically modified pulp fiber of the present embodiment having a part of the structural units of cellulose having the above general formula (2) (SO ₃ ⁻ Z introduced into cellulose) will be specifically described.

First, as a reaction solution, a solution obtained by dissolving sulfamic acid and urea in water can be used. Hereinafter, the state in which the reaction solution (sulfamic acid and urea) is brought into contact with the fiber raw material in the contacting step is referred to as the reaction solution-impregnated fiber.
Urea contained in the reaction solution mainly functions as a catalyst.

(Mixing ratio of reaction solution)
When adopting the method of impregnating the fiber raw material with the reaction liquid by immersing the fiber raw material in the reaction liquid, the mixing ratio of sulfamic acid and urea contained in the reaction liquid is not particularly limited. For example, the mixing ratio described in Examples described later can be used.

(Contact amount of reaction liquid)
The amount of the reaction liquid brought into contact with the fiber raw material is such that the sulfamic acid and urea in the reaction liquid are brought into contact with the fiber raw material at a predetermined ratio.
Specifically, the fiber material in the reaction liquid-impregnated fiber is contacted so that the amount of sulfamic acid in the reaction liquid and the amount of urea in the reaction liquid are appropriate when subjected to the reaction step described later.

For example, the contact amount of sulfamic acid is adjusted so that the value obtained by dividing by the contact amount of sulfamic acid and urea is 0.8 or more. Specifically, the reaction solution is prepared so that the mixing ratio of sulfamic acid and urea is sulfamic acid/urea≧0.8 in mass ratio.

For example, the contact amount of sulfamic acid is adjusted so that the value obtained by dividing the contact amount of sulfamic acid by the contact amount of urea is 0.8 or more. Specifically, the reaction solution is prepared so that the mixing ratio of sulfamic acid and urea is sulfamic acid/urea≧0.8 in mass ratio. More preferably, the reaction solution is prepared such that the mixing ratio of sulfamic acid and urea is 0.8 or more and 4.0 or less, more preferably 1.0 or more and 4.0 or less, in mass ratio.
More specifically, the contact amount of sulfamic acid is adjusted to 60 parts by mass or more with respect to 100 parts by mass of the solid content of the fiber raw material in the reaction liquid-impregnated fibers immediately before being subjected to the heating reaction. This value is preferably adjusted to 60 parts by mass or more and 250 parts by mass or less.

On the other hand, the contact amount of urea is 100% of the solid content mass of the fiber raw material while maintaining the above relationship with sulfamic acid with respect to the solid content mass of the fiber raw material in the fiber impregnated with the reaction liquid immediately before being subjected to the heating reaction. Adjust to 20 parts by mass or more with respect to parts by mass. This value is preferably 30 parts by mass or more, more preferably 50 parts by mass or more. In addition, as an upper limit, it prepares so that it may become 250 mass parts or less, preferably 200 mass parts or less, for example.

The contact amount of sulfamic acid and the contact amount of urea with respect to 100 parts by mass of the solid content of the fiber raw material are appropriately calculated according to the state of the reaction liquid-impregnated fibers when subjected to the reaction step described later. For this specific calculation method, for example, a calculation method described in Examples to be described later can be adopted.

As for the state of the reaction liquid-impregnated fiber when subjected to the reaction process of the next step, for example, the reaction liquid-impregnated fiber is in the state that it is, that is, in the state that the fiber raw material and the reaction liquid are in contact. Examples include a state in which no treatment is performed, and a state in which water is actively removed from a state in which the fiber raw material and the reaction liquid are brought into contact with each other.

The former (a state in which moisture is not actively removed), the fiber impregnated with the reaction liquid, includes a state in which the fiber raw material and the reaction liquid are in contact (for example, including a slurry state), or a state in which the reaction liquid and the fiber raw material are in contact with each other. It means that it includes those prepared by taking out the fiber raw material from the state in which it is in contact with and leaving it to stand.
On the other hand, the latter (a state in which water is actively removed), the reaction liquid-impregnated fiber, refers to a fiber in which the water is intentionally removed from the state in which the fiber raw material and the reaction liquid are brought into contact. A product prepared by taking out the fiber raw material from the state in which the raw material is in contact and air-drying it naturally, a product prepared by dehydrating and filtering the state in which the reaction liquid and the fiber raw material are in contact, and a product obtained by dehydrating and filtering. further air-dried, prepared by further drying this dehydrated and filtered product using a circulating air dryer, and further dried using a heated dryer to prepare this dehydrated and filtered product and those prepared by contacting the reaction liquid and the fiber raw material with a circulating air dryer or a heating dryer.

For this reason, the reaction liquid-impregnated fibers when subjected to the reaction step are in a state in which the above-mentioned active water removal is not performed, or in a state in which a certain amount of water is removed by active water removal. good. Further, when the moisture is removed by drying, there is no particular problem even if the moisture content after drying is about 1%.
In particular, if the latter method is adopted, the water content in the reaction liquid-impregnated fibers can be reduced when supplied to the reaction step, so that the reaction time in the heating reaction in the reaction step can be shortened. Therefore, an advantage is obtained that the productivity of chemically modified pulp fibers can be improved. Further, if a method of performing dehydration treatment is employed, there is an advantage that the reaction liquid-impregnated fiber can be prepared more efficiently than when a large amount of reaction liquid is treated.

In the case of adopting a method of actively drying, the moisture content of the reaction liquid impregnated fiber may be dried to about 1%, and moisture is removed by a method of drying to an absolute dry state considerably lower than 1%. may
In the present specification, a non-absolutely dry state in which the moisture content of the reaction liquid-impregnated fibers is 1% or more is also referred to as a wet state. For example, in the specification of the present application, a wet state may be used not only in a state of being impregnated with a reaction liquid or the like, or in a state of being dehydrated to some extent, but also of being in a state of being dried to some extent.
In addition, absolute drying in this specification means, for example, reducing the pressure in a desiccator or the like containing a desiccant such as calcium chloride or diphosphorus pentoxide, or performing heat drying treatment for a long time to reduce the moisture content to less than 1%. It means something in a lowered state.
Therefore, when the latter method is adopted in the contacting step, the moisture content of the reaction liquid-impregnated fibers may be set to a non-absolute dry state, or a method to make the moisture content of the reaction liquid-impregnated fibers to an absolute dry state may be adopted. However, it is preferable to adopt a non-absolute dry method.

In addition, the moisture content in this specification is calculated using the following formula.

Moisture content (%) = 100 - (solid mass (g) in reaction liquid-impregnated fiber / reaction liquid-impregnated fiber (g) at the time of moisture content measurement) x 100

The state of the fiber raw material when the reaction liquid is brought into contact is not particularly limited. For example, it may be in a dry state or in a wet state (that is, wet state).

(Reaction step)
The reaction solution-impregnated fibers prepared in the contacting step as described above are supplied to the next reaction step.
The reaction step in the chemical treatment step is a step of reacting cellulose, sulfamic acid, and urea contained in the fiber raw material in the reaction liquid-impregnated fibers supplied from the contact step. Specifically, it is a step of introducing a predetermined substituent into the cellulose that constitutes the pulp or the like contained in the reaction solution-impregnated fiber.

This reaction step is not particularly limited as long as it is a reaction capable of introducing SO ₃ ^-Z into the cellulose in the fiber raw material of the reaction solution-impregnated fiber.
For example, a method (heating reaction) of accelerating the reaction by heating the reaction solution-impregnated fibers can be employed. Below, in the reaction step, a manufacturing method using a heating reaction will be described as a representative.

(Reaction temperature in reaction step)
The reaction temperature in the reaction step is not particularly limited as long as it is a temperature at which SO ₃ ^−Z can be introduced into the cellulose constituting the fiber raw material while suppressing the thermal decomposition and hydrolysis reaction of the fiber.
For example, the ambient temperature of the reaction liquid-impregnated fibers supplied to the reaction step is adjusted to 100° C. or higher and 200° C. or lower. The ambient temperature is preferably 120° C. or higher and 200° C. or lower.
If the ambient temperature during heating is higher than 200° C., thermal decomposition of the fibers may occur, or discoloration of the fibers may accelerate. On the other hand, when the reaction temperature is lower than 100° C., the transparency of the obtained fiber after the reaction tends to be low.
Therefore, from the viewpoint of improving the transparency of the fibers obtained after the reaction, the reaction temperature (specifically, the ambient temperature) in the reaction step is preferably 100° C. or higher and 200° C. or lower. It is more preferably 120° C. or higher and 180° C. or lower, and still more preferably 120° C. or higher and 160° C. or lower.

The heater or the like used in the reaction step is not particularly limited as long as it can directly or indirectly heat the reaction liquid-impregnated fibers after the contact step while satisfying the above requirements.
For example, a hot press method using a known dryer, vacuum dryer, microwave heating device, autoclave, infrared heating device, or heat press (for example, AH-2003C manufactured by AS ONE Co., Ltd.) can be employed. can be done. In particular, from the viewpoint of operability, it is preferable to use a circulating air dryer because gas may be generated in the reaction process.

(Reaction time in reaction step)
The heating time (that is, the reaction time) when the above heating method is employed as the reaction step is not particularly limited as long as SO ₃ ⁻ Z can be appropriately introduced into the cellulose constituting the reaction solution-impregnated fiber.
For example, the reaction time in the reaction step can be adjusted to 1 minute or more when the reaction temperature is adjusted to fall within the above range. The time is preferably 5 minutes or longer, more preferably 10 minutes or longer, and still more preferably 15 minutes or longer.
If the reaction time is shorter than 1 minute, it is presumed that the substitution reaction on cellulose has hardly progressed. On the other hand, even if the heating time is too long, there is a tendency that an increase in the introduction amount of SO ₃ ^-Z cannot be expected.
Therefore, the reaction time when the above heating method is employed as the reaction step is preferably 5 minutes or more and 300 minutes or less from the viewpoint of reaction time and operability. More preferably, it should be 5 minutes or more and 120 minutes or less.

(Pre-drying step of contact step)
In the above example, in the method for preparing the reaction liquid-impregnated fiber in the contacting step, the method for preparing the reaction liquid-impregnated fiber in a state in which water has been actively removed has been described. (Pre-drying step) is used (for example, when the reaction liquid and the fiber raw material are in contact with each other and are directly heated and dried, or when the dehydrated product is heated and dried), the heating temperature is It is desirable to adjust so that the temperature is below a predetermined temperature.
The drying temperature in this pre-drying step is not particularly limited as long as it can remove moisture contained in the reaction solution-impregnated fibers and surrounding moisture and is adjusted to a temperature at which the above reaction does not proceed.
For example, the drying temperature in the preliminary drying step can be adjusted so that the ambient temperature of the reaction liquid-impregnated fibers is 100° C. or less. On the other hand, from the viewpoint of workability, it is preferable to adjust the temperature to 50° C. or higher.
Therefore, the drying temperature in the preliminary drying step in the contact step is preferably adjusted to 50°C or higher and 100°C or lower, more preferably 70°C or higher and 100°C or lower.

(fiber raw material)
The fiber raw material used in this manufacturing method is not particularly limited as long as it contains cellulose as described above.
For example, what is generally called pulp may be used, and what contains cellulose isolated from sea squirts, seaweed, etc. can be used as the fiber raw material, but as long as it is composed of cellulose molecules, , can be anything.
Examples of the above-mentioned pulp include wood-based pulp (made from conifers, broad-leaved trees, etc.) (hereinafter simply referred to as wood pulp), dissolving pulp, cotton-based pulp such as cotton linter, straw, bagasse, kozo, Examples include, but are not limited to, mitsumata, hemp, kenaf, non-wood pulp such as fruit, and waste paper pulp produced from waste newspapers, waste magazines, waste cardboard, and the like. From the standpoint of availability, wood pulp is easy to employ as a fiber raw material.

There are various types of this wood pulp, but there is no particular limitation in use. Examples thereof include softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), thermomechanical pulp (TMP), and other papermaking pulps.
When the above pulp is used as the fiber raw material, one type of the pulp described above may be used alone, or two or more types may be mixed and used.

(Moisture adjustment step in contact step)
The contacting step may include a moisture adjusting step so that the moisture content of the fiber raw material to be brought into contact with the reaction liquid falls within a predetermined range.
This moisture adjustment step is a step of drying or moistening the fiber raw material so that it has a predetermined moisture content, thereby adjusting it to have a desired moisture content. By including this moisture adjustment step, the moisture content in the fiber raw material can be homogenized to some extent when brought into contact with the reaction solution or the like, so there is a possibility of improving the product stability in continuous operation.
Moreover, if the fiber material is dried to some extent to reduce the moisture content (for example, the moisture content is 1% or more and 10% or less), there is an advantage that storage stability can be improved.

(Washing process after reaction process)
A washing step for washing the fibers after the reaction may be included after the reaction step in the chemical treatment step.
The surface of the fiber after introduction of SO ₃ ^-Z may be acidic due to the influence of sulfamic acid and the like. Also, if the reaction solution is brought into contact with the substrate excessively, unreacted reaction solution may remain. In such a case, it is possible to improve the handleability by providing a washing step to reliably complete the reaction and remove the excess reaction solution to neutralize the solution.

This washing step is not particularly limited as long as the washing can be carried out so that the washing water becomes substantially neutral when the fibers after the reaction are washed with water.
For example, the fiber may be washed with pure water or the like until the fiber after the reaction becomes neutral, or may be neutralized and washed with an alkali or the like.
In addition, when performing neutralization cleaning, an inorganic alkaline compound, an organic alkaline compound, etc. can be mentioned as an alkaline compound contained in an alkaline solution. Examples of inorganic alkali compounds include hydroxides, carbonates, and phosphates of alkali metals. Examples of organic alkali compounds include ammonia, aliphatic amines, aromatic amines, aliphatic ammoniums, aromatic ammoniums, heterocyclic compounds, and hydroxides of heterocyclic compounds.

By using the production method as described above, it is possible to obtain the chemically modified pulp fiber of the present embodiment in which the anionic substituent SO ₃ ⁻ Z is introduced within a predetermined range as described above. For example, the introduction amount of SO ₃ ⁻ Z, which is an anionic substituent, in the chemically modified pulp fiber of the present embodiment is 0.8 mmol/g or more and 7 mmol/g or less.

In particular, it is preferable that the chemically modified pulp fiber of the present embodiment produced by the production method as described above has a structure capable of expanding and contracting in the radial direction of the fiber. Specifically, the chemically modified pulp fiber of the present embodiment expands in the radial direction of the fiber when moisture is absorbed (diameter expansion), and shrinks in the radial direction of the fiber when moisture is removed (diameter contraction). Structured ones are preferred.
The rate of change in the radial direction of this fiber is formed to be different from that of general pulp fibers. For example, general pulp fibers have a rate of change of about 1.1 from the dry state to the swollen state when water is absorbed, whereas the chemically modified cellulose fine fibers of the present embodiment have a rate of change of about 1.1 from this value. are formed in such a structure that the rate of change in the radial direction is large. Specifically, the chemically modified cellulose fine fibers of this embodiment are fibers having a structure in which the rate of change in the radial direction of the fiber is greater than 1.1 and can be expanded or contracted in the range of 10 or less. be.
The structure in which this chemically modified pulp fiber expands and contracts in the radial direction will be described in detail below.

The rate of change of the chemically modified pulp fibers of this embodiment will be described.
The rate of change is a value obtained by dividing the average swollen fiber width of the chemically modified pulp fibers of the present embodiment after absorbing water by the average non-swollen fiber width of the chemically modified pulp fibers of the present embodiment in a dry state.

(Method for measuring average swollen fiber width)
First, a method for roughly calculating the average swollen fiber width will be described.
The average swollen fiber width is calculated by averaging the swollen fiber widths measured using a polarizing microscope for a dispersion liquid in which the chemically modified pulp fiber of the present embodiment is adjusted to have a solid content concentration of 0.1% by mass. can be done. For example, it is calculated by dividing the total swollen fiber width of 10 fibers by 10.
For the detailed calculation method of the average swollen fiber width, refer to the method described in Examples.

The average swollen fiber width of the chemically modified pulp fiber of this embodiment may vary depending on the fiber raw material.
For example, when softwood is used as a raw material, the chemically modified pulp fibers of the present embodiment are formed so as to have an average swollen fiber width of 50 μm or more. The thickness is preferably 60 μm or more, more preferably 70 μm or more, further preferably 80 μm or more. Further, when hardwood is used as a raw material, the chemically modified pulp fibers of the present embodiment are formed so as to have an average swollen fiber width of 50 μm or more. The thickness is preferably 60 μm or more, more preferably 70 μm or more, further preferably 80 μm or more.

An arbitrary single fiber is selected from a polarizing microscope photograph of the fibers of the dispersion liquid taken using a polarizing microscope.
In this fiber, find the point where the fiber width is the widest. Next, the maximum fiber width (swollen fiber width referred to in this specification) at this point is measured. Similarly, 10 swollen fiber widths are measured from the polarizing micrograph. The average swollen fiber width can be calculated by dividing the sum of the swollen fiber widths of the obtained 10 fibers by 10.

(Method for measuring average non-swollen fiber width)
Next, a method for roughly calculating the average non-swollen fiber width will be described.
The average non-swollen fiber width can be calculated by averaging the non-swollen fiber widths measured using an electron microscope for the chemically modified pulp fibers of the present embodiment in a dried state (dry state). For example, it is calculated by dividing the total non-swollen fiber width of 10 fibers by 10.
For the detailed calculation method of the average non-swollen fiber width, refer to the method described in Examples.

The chemically modified pulp fibers of the present embodiment are dried to a predetermined state.
An arbitrary single fiber is selected from an electron micrograph of the chemically modified pulp fiber of this embodiment in a dry state taken with an electron microscope. In this fiber, find the point where the fiber width is the widest. Next, the maximum fiber width (non-swollen fiber width referred to in this specification) at this point is measured. Similarly, ten unswollen fiber widths are measured from electron micrographs. The average unswollen fiber width can be calculated by dividing the sum of the unswollen fiber widths of the 10 fibers obtained by 10.

It should be noted that the fiber raw material used in this production method may partially contain fibers having a non-swollen fiber width greater than 60 μm.
For example, when broad-leaved trees are used as a raw material, fibers with a non-swelling fiber width of about 140 μm such as vessels (vessels) are included. If such fibers are arbitrarily counted and the average non-swollen fiber width is calculated, the numerical value of the average non-swollen fiber width becomes too large to obtain a true value.
For this reason, the swollen fiber width used to calculate the average non-swollen fiber width is calculated from these fibers by observing 100 or more fibers in advance, selecting 10 fibers excluding elements that clearly give errors. do.

Also, the average non-swollen fiber width of the chemically modified pulp fibers of the present embodiment may vary depending on the fiber raw material.
For example, when softwood is used as a raw material, the chemically modified pulp fibers of the present embodiment are formed so that the average non-swollen fiber width is 20 μm or more and 50 μm or less. The thickness is preferably 20 μm or more and 40 μm or less, more preferably 20 μm or more and 30 μm or less. Further, when hardwood is used as a raw material, the chemically modified pulp fibers of the present embodiment are formed so that the average non-swollen fiber width is 10 μm or more and 60 μm or less. The thickness is preferably 20 μm or more and 40 μm or less, more preferably 20 μm or more and 30 μm or less.

The chemically modified pulp fiber of the present embodiment used for measuring the non-swollen fiber width is not particularly limited as long as it is in a dry state in terms of appearance.
For example, the moisture content of the chemically modified pulp fibers of the present embodiment is preferably 20% or less, more preferably 15% or less. The lower limit is not particularly limited, and for example, it may be in an absolutely dry state (moisture content is 0%).
When measuring the non-swollen fiber width of the chemically modified pulp fiber of the present embodiment, the drying method is not particularly limited as long as the moisture content can be adjusted within the above range. For example, in addition to natural drying, drying may be performed using heat drying, vacuum freeze drying, desiccator, or the like.
Moreover, the moisture content can be calculated by the same method as the method for calculating the moisture content of the pulp described in the Examples.

Moreover, the chemically modified pulp fiber of the present embodiment also has a structure that exhibits a predetermined recovery rate.
Specifically, the chemically modified pulp fiber of the present embodiment has a structure that can be restored with a restoration rate in the range of 0.6 or more and 1.5 or less. This recovery rate is preferably 0.7 or more and 1.4 or less, more preferably 0.8 or more and 1.3 or less.

This recovery rate is defined as the average non-swollen fiber width of the chemically modified pulp fiber of the present embodiment, and the average non-swollen fiber width in the state in which the dried fiber is swollen by absorbing water and dried again. and shows the relationship between

The recovery rate can be calculated using the following formula.

Restoration rate = (average non-swollen fiber width β when the fibers swollen by absorbing water in the chemically modified pulp fiber A of this embodiment in a dry state are dried again) / (chemical of this embodiment in a dry state Average non-swollen fiber width α of modified pulp fiber A)

The "chemically modified pulp fiber A of the present embodiment in a dry state" in the numerator of the formula and the "chemically modified pulp fiber A of the present embodiment in a dry state" in the denominator are the same fiber.
In the formula, "fibers that have been swollen by absorbing water" means that a dispersion liquid is prepared by adjusting the chemically modified pulp fiber A of the present embodiment in a dry state so that the solid content concentration is 0.1% by mass. , the fiber after standing for a predetermined time (eg, 30 minutes).
In the formula, the moisture content of the “chemically modified pulp fiber A of the present embodiment in a dry state” and the fiber “when dried again” are the same value or a similar value (for example, within ± 10%). adjust to

(When the structural unit has the general formula (3))
A case where a part of the structural units of cellulose in the chemically modified pulp fiber of the present embodiment has the general formula (3) will be described below.

The method for measuring the average swollen fiber width, the method for measuring the average non-swollen fiber width, the method for calculating the recovery ratio, and the like are measured or calculated in the same manner as when the substituent is SO ₃ ^−Z .

A TEMPO oxidation catalytic reaction can be employed to introduce CO ₂ ^−Z into D-glucose, which is a structural unit of cellulose that constitutes the fiber raw material. TEMPO (or its derivative)-catalyst/sodium bromide-oxidizing agent/sodium hypochlorite-oxidizing agent are brought into contact with the fiber raw material in water, and CO ₂ ^- Z is introduced by reacting at room temperature. . Concerning the specific operation of this TEMPO oxidation catalytic reaction, for example, Tsuguyuki Saito, Satoshi Kimura, Yoshiharu Nishiyama and Akira Isogai, Biomacromolecules, 8 (8), 2485-2491 (2007) can be referred to.

(TEMPO oxidation catalyst)
A derivative having a molecular skeleton of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl may be used as the TEMPO oxidation catalyst used when oxidizing the fiber raw material. Specifically, compounds that generate 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine-N-oxy radicals are preferred.

(Promoting agent)
As the bromide or iodide used for oxidizing the fiber raw material, compounds that can be dissociated and ionized in water, such as alkali metal bromides and alkali metal iodides, can be used. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction.

(Oxidant)
The oxidizing agent used for oxidizing the fiber raw material is an oxidizing agent capable of promoting the desired oxidation reaction, such as halogen, hypohalous acid, halogenous acid, perhalogen acid or salts thereof, halogen oxides, and peroxides. Any oxidizing agent, if present, can be used. Among them, from the viewpoint of production cost, sodium hypochlorite, which is currently most widely used in industrial processes and is inexpensive and has a low environmental load, is particularly preferable.

Since the TEMPO oxidation catalytic reaction allows the oxidation reaction of the fiber raw material to proceed smoothly and efficiently even under mild conditions, the reaction temperature may be room temperature of about 15 to 30°C. As the reaction progresses, carboxyl groups are formed in the cellulose, so the pH of the reaction solution decreases. It is desirable to maintain the pH of the liquid at about 9-12, preferably about 10-11.
The end point of the reaction is desirably carried out until no decrease in pH is observed. However, about 2 hours is desirable from the viewpoint of production efficiency and that if the fiber raw material is brought into contact with the alkaline solution for a long period of time, the fiber may be decomposed to shorten the fibers.

(Chemically modified pulp fiber of the present embodiment having at least the above general formula (3) in the cellulose structural unit)
The chemically modified pulp fiber of the present embodiment produced by the production method as described above is a pulp fiber having at least the above general formula (3) in the structural unit of cellulose as described above. The fiber has a structure in which the change rate in the radial direction of the fiber is larger than 1.1 and can be expanded or contracted in the range of 10 or less.
In addition, the amount of the anionic substituent introduced into the chemically modified pulp fiber of the present embodiment is, for example, 0.8 mmol/g or more and 7 mmol/g or less.

In addition, the chemically modified pulp fiber of the present embodiment has the above general formula (3) in the structural unit of cellulose as described above, and the above-described hydroxyl groups are bonded at the 2-, 3-, and 6-positions. A part of the structural unit may have a structure in which CO ₂ ^-Z is directly bonded to some or all of the carbons.

(When the structural unit has the general formula (4))
A case where a part of the structural units of cellulose in the chemically modified pulp fiber of the present embodiment has the above general formula (4) will be described below.

The method for measuring the average swollen fiber width, the method for measuring the average non-swollen fiber width, the method for calculating the recovery ratio, and the like are measured or calculated in the same manner as when the substituent is SO ₃ ^−Z .

In order to introduce PO ₃ ^2- Z into D-glucose, which is a structural unit of cellulose composing pulp fibers, a fiber raw material, a phosphorylation reaction can be employed. Ammonium dihydrogen phosphate-phosphorylating agent/urea-catalyst is brought into contact with the fiber raw material in water, and PO ₃ ^- Z is introduced by heating at 120°C to 180°C. For specific operations of this phosphorylation reaction, for example, Yuichi Noguchi, Ikue Homma and Yusuke Matsubara, Cellulose, 24, 1295-1305 (2017) can be referred to.

(Phosphorylating agent)
When a compound having a phosphoric acid-derived group is used as the compound that reacts with the fiber raw material, it is not particularly limited, but it consists of phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, or salts or esters thereof. At least one selected from the group. Among these, compounds having PO ₃ ^- Z are preferable because they are low in cost and easy to handle, but they are not particularly limited.

The compound having PO ₃ ^- Z is not particularly limited, but examples include phosphoric acid, lithium dihydrogen phosphate which is a lithium salt of phosphoric acid, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. be done. Furthermore, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate and sodium polyphosphate, which are sodium salts of phosphoric acid, may be mentioned. Furthermore, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate, which are potassium salts of phosphoric acid, may be mentioned. Furthermore, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate, etc., which are ammonium salts of phosphoric acid, can be used.
Among these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, and ammonium phosphoric acid are preferred from the viewpoint of high efficiency of PO ₃ ^- Z introduction and easy industrial application, and dihydrogen phosphate. Sodium, disodium hydrogen phosphate, and ammonium dihydrogen phosphate are more preferred, and ammonium dihydrogen phosphate is even more preferred, but are not particularly limited.

(PO ₃ ^- Z introduction step)
A method of heating is particularly effective for accelerating the reaction when introducing PO ₃ ^-Z into the fiber raw material. The heat treatment temperature for introduction of PO ₃ ^-Z is not particularly limited, but it is preferably in a temperature range in which thermal decomposition, hydrolysis, etc. of the fiber raw material are unlikely to occur. For example, when a fiber raw material containing cellulose is selected as the fiber raw material, the temperature is preferably 250° C. or less from the viewpoint of thermal decomposition temperature, and the heat treatment at 100 to 180° C. is preferable from the viewpoint of suppressing hydrolysis of cellulose. preferable. Moreover, the heat treatment time is desirably short from the viewpoint of suppressing thermal decomposition, hydrolysis, etc. of the fiber raw material and from the viewpoint of production efficiency, specifically within 2 hours.

(Chemically modified pulp fiber of the present embodiment having at least the above general formula (4) in the cellulose structural unit)
The chemically modified pulp fiber of the present embodiment produced by the production method as described above is a pulp fiber having at least the above general formula (4) in the structural unit of cellulose as described above. The fiber has a structure in which the change rate in the radial direction of the fiber is larger than 1.1 and can be expanded or contracted in the range of 10 or less.
In addition, the amount of the anionic substituent introduced into the chemically modified pulp fiber of the present embodiment is, for example, 0.8 mmol/g or more and 7 mmol/g or less.

In addition, the chemically modified pulp fiber of the present embodiment has the above general formula (4) in the structural unit of cellulose as described above, and in addition, the above-described hydroxyl groups are bonded at the 2-, 3-, and 6-positions. A part of the structural unit may have a structure in which PO ₃ ^2- Z is directly bonded to some or all of the carbons.

The present invention will be explained in detail by way of examples. However, the present invention is in no way limited by the following examples.

(Experiment 1)
First, chemically modified pulp fibers to be contained in the gas barrier sheet of the present invention will be described.

(fiber raw material)
Softwood bleached kraft pulp (NBKP) manufactured by Marusumi Paper Co., Ltd. was used as a fiber raw material. NBKP had an average fiber length of 2.57 mm and an average swollen fiber width of 28 µm. Also, this NBKP was used as a comparative example of physical properties (Sample I). Below, the NBKP used in the experiment will be simply described as pulp.

The pulp has an electrical conductivity value in the range of 0.1 to 0.2 μS/cm measured with a large amount of ion-exchanged water (ion-exchanged water generator manufactured by Organo Co., model number: G-5DSTSET). hereinafter referred to as pure water), drained with a stainless steel sieve with an opening of 75 μm (200 mesh), and adjusted to a solid content concentration of 25.0% by mass. (simply referred to as wet pulp) was subjected to the experiment. That is, 400 g of wet pulp used in the experiment contained 100 g of pulp.

(Chemical treatment process)
A chemically modified pulp fiber having the above general formula (2) as a constitutional unit, in which SO ₃ ⁻ Z as an anionic substituent was introduced into cellulose in the fiber raw material, was obtained by performing the following chemical treatment steps.

In the experiment, first, the pulp was placed in a container containing the reaction liquid, and the pulp was impregnated with the reaction liquid. This corresponds to the "contact step" in the "chemical treatment step" of the present embodiment.
In the experiment, anionic SO ₃ ⁻ Z was introduced into D-glucose, which is a structural unit of cellulose in the fiber raw material.

A reaction solution was prepared as follows.
Put 600 mL of pure water in a 1 L beaker, and add sulfamic acid (purity 99.8%, manufactured by Fuso Chemical Industry Co., Ltd.) and urea (purity 99.0%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number; special grade reagent) in the following ratio. added. Sulfamic acid (g)/urea (g) = 70/35 (Sample A), 120/60 (Sample B), 180/90 (Sample C), 240/120 (Sample D), 180/45 (Sample E) , 180/180 (Sample F), 60/30 (Sample G), 180/270 (Sample H). Sulfamic acid and urea were stirred at room temperature until completely dissolved to prepare a reaction solution.
400 g of wet pulp was added to the obtained reaction liquid and impregnated for about 10 minutes.

The “solid mass (g)” of pulp refers to the dry weight of the pulp itself to be measured.
The weight of the dried pulp was measured by drying at 105° C. for 2 hours using a drier until the moisture content reached equilibrium.
The method of evaluating the equilibrium state in the experiment is to set the temperature of the constant temperature bath to a predetermined temperature (e.g., 50 ° C. or 105 ° C.) in the above dryer for 1 hour, and then measure the weight twice in succession. A state in which the amount of change was within 1% of the weight at the start of drying was considered to be in an equilibrium state (however, the second weight measurement was made to be at least half the drying time required for the first time).
The measurement of moisture content was calculated by the following formula.

Moisture content (%) = 100 - (solid mass of pulp (g)/pulp mass (g) at moisture content measurement) x 100

The pulp impregnated with the reaction liquid was taken out from the container and dried in a dryer at 80° C. to prepare reaction liquid-impregnated pulp (corresponding to the “reaction liquid-impregnated fiber” of the present embodiment).

Next, the prepared reaction liquid-impregnated pulp was subjected to a reaction step using heating (corresponding to the "reaction step" in the "chemical treatment step" of the present embodiment).
The reaction conditions were as follows.
For heating, the temperature of the constant temperature bath of the dryer using a dryer: 140 ° C., heating time: 30 minutes

After the heat reaction, the reaction solution-impregnated pulp was washed until it became neutral to obtain chemically modified pulp fibers.

(Preparation of dispersion)
A pulp slurry having a solid content concentration of 1.0% by mass was prepared by dispersing chemically modified pulp fibers in water.
The solid content concentration was calculated by the following formula.

Solid content concentration (%) = (solid mass of pulp (g) / mass of pulp slurry (g)) x 100

(Measurement of introduced amount of SO ₃ ^- Z)
The amount of SO ₃ ⁻ Z introduced into the obtained chemically modified pulp fiber was measured by electrical conductivity measurement.
The chemically modified pulp fiber is a salt in which Na is bound by electrostatic interaction due to the influence of sodium bicarbonate used for neutralization. In this state, the electrical conductivity cannot be measured, so it is necessary to remove the Na salt once to form an H-type with protons bonded. Therefore, the prepared chemically modified pulp fiber was first converted to the H type as follows, and then measured by titration with an aqueous sodium hydroxide solution.

50 g of pulp slurry (0.5 g of solid mass) was placed in a beaker, and 250 mL of hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., model number; special grade reagent) diluted with pure water and adjusted to 0.5 M was added to the beaker. added. The shaking treatment was performed for 1 hour or more. Thereafter, the mixture was poured onto a mesh (300 mesh) with an opening of 46 μm, and washed with a large amount of water to prepare H-type chemically modified pulp fibers.
The prepared H-type chemically modified pulp fibers were placed in a beaker so that the mass of the solid content was 0.2 g, and pure water was added to make the total amount 50 g. This beaker was set in an electrical conductivity meter (water quality meter (manufactured by Toa DKK Co., model number: MM-43X) and electrical conductivity electrode (manufactured by Toa DKK Co., Ltd., model number: CT-58101B) was used) to introduce functional groups. amount was measured.

In the titration using alkali, 20 μL to 100 μL of a solution obtained by diluting a 5M sodium hydroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name; 5 mol/L sodium hydroxide solution) with pure water to 1M was added dropwise. A curve was obtained by plotting the electrical conductivity on the vertical axis and the titration amount of sodium hydroxide on the horizontal axis, and the inflection point was confirmed from the obtained curve. At the beginning of dropping, the electrical conductivity decreases, but shows an inflection at a certain point. Since the titration amount of sodium hydroxide required up to this inflection point corresponds to the amount of SO ₃ ⁻ Z, the sodium hydroxide amount at this inflection point is divided by the pulp solid content mass of the chemically modified pulp fiber used for measurement. By doing so, the amount of SO ₃ ^-Z in the chemically modified pulp fiber, that is, the amount of SO ₃ ^-Z introduced was measured.

(Measurement of total light transmittance of chemically modified pulp fiber)
The total light transmittance was measured using the pulp slurry for measurement.
A predetermined amount is collected from the pulp slurry for measurement, and the collected measurement solution is set in a spectroscopic haze meter (manufactured by Nippon Denshoku Industries, model number SH-7000, Ver2.00.02) to measure the total light transmittance. was measured as follows. In addition, the measuring method was performed based on the method of JISK7105.
An optional glass cell (part number: 2277, square cell, optical path length 10 mm x width 40 x height 55) of the spectroscopic haze meter containing pure water was used as a blank measurement value, and the light transmittance of the pulp slurry for measurement was measured. bottom. The light source was D65, the field of view was 10°, and the measurement wavelength range was 380 to 780 nm.
The total light transmittance (%) was calculated using the numerical value obtained by the control unit of the spectroscopic haze meter (model number CUII, Ver2.00.02).

(Measurement of swollen fiber width of chemically modified pulp fiber)
A sample was taken from the prepared pulp slurry (dispersion) to prepare a sample liquid having a solid concentration of 0.1% by mass. The pH of the sample liquid was adjusted to be within the range of 5-7. The pH used in this experiment is simply the pH of pure water, not a pH-adjusted solution such as a buffer solution.
From this sample solution, 50 to 100 μL of a measurement sample was dropped onto a slide glass, covered with a cover glass, and photographed using a polarizing microscope (eg, ECLIPSE LV100ND manufactured by Nikon Corporation). Shooting was performed at 5 or more locations at random.
The fiber width of the chemically modified pulp fiber in a swollen state (swollen fiber width) was measured by the following measurement method from the fiber of the photographed polarizing microscope photograph.
Select one fiber from the picture. Find the largest point in the radial direction (width direction) of this fiber. The longest distance at this point is measured, and this distance is taken as the swollen fiber width.
The method of measuring the distance is, for example, to draw a tangent line to the portion facing the outside of the above-mentioned location, draw a perpendicular line to this tangent line based on the point of contact, and take the point of intersection with the other outer surface that intersects the perpendicular line as the intersection point. The swollen fiber width can be measured by measuring the distance between the contact points and the intersection points.

The average swollen fiber width was calculated by dividing the sum of the swollen fiber widths of the 10 fibers by 10.

(Measurement of average fiber length and short fiber rate of chemically modified pulp fiber)
Pulp slurry for measurement (0.1 g solid mass) was placed in a plastic beaker, and water was added to this beaker to prepare a total volume of 300 mL of thin pulp slurry.
This thin pulp slurry was measured using a fiber length distribution measuring instrument (manufactured by Valmet, model number: FS-5) to determine the average fiber length of the chemically modified pulp fibers in the thin pulp slurry and the short fiber rate at 0.04 mm to 0.20 mm. was measured. The accuracy of the measurement was performed in the mode conforming to the ISO standard of the device.

(Experimental result)
FIG. 2 shows physical property values of samples A to I.
In Experiment 1, a chemically modified pulp fiber having the above general formula (2) as a structural unit of cellulose, which is a raw material for a gas barrier sheet to be described later, was prepared. The oxygen permeability of this chemically modified pulp fiber was evaluated as the gas barrier property of a gas barrier sheet to be described later.

(Experiment 2)
Next, the gas barrier sheet of the present invention using the chemically modified pulp fibers prepared in Experiment 1 will be described.

(Preparation of sheet)
A specific method for producing the sheet will be described below.
The method for producing the gas barrier sheet used in the experiment was as follows.
First, the pulp slurry for measurement is placed in a 5 L plastic container, and the sheet material samples A to I are weighed so that the size is 25 cm × 25 cm and the basis weight is 7 to 100 g / m 2, and the solid content concentration is 0.2 to 0.5. Tap water was added and dispersed well until it reached mass %. This diluted slurry is JIS P 8222 Pulp-Preparation method for hand-made paper for testing-(2015), and a nylon mesh (manufactured by AS ONE Co., Ltd., A sheet was formed by using a wire mesh pasted with model number PA-46μ, opening 46μm.
The resulting sheet was cut into sizes required for the evaluation of the properties described below and used.

Specifically, Sample A (Examples 1-3), Sample B (Examples 4-6), Sample C (Examples 7-9, Comparative Examples 4-5), Sample D (Examples 10-12) , Sample E (Examples 13-15), Sample F (Examples 16-18), Sample G (Comparative Examples 1-3), Sample H (Comparative Examples 6-8), Sample I (Comparative Examples 9-11) were used to prepare sheets with different basis weights.

(Measurement of sheet basis weight, thickness and density)
Based on JIS P 8184 (2011), the sheet basis weight (g/m ² ) was calculated by dividing the mass of the sheet obtained with an electronic balance by the area of the sheet.
The thickness of the sheet conforms to JIS P 8118 (2014), and the thickness (μm) was measured with a micrometer (manufactured by TECLOK, model number: PG-02). The density (g/cm ³ ) was calculated by dividing the obtained sheet basis weight by the thickness.
The sheet had a moisture content of about 5 to 15%.

(Oxygen permeability evaluation)
The obtained gas barrier sheet was used to evaluate gas barrier properties.
As a gas barrier property, oxygen permeability (cc/m ² ·24 hours · atm) was measured by a method based on JIS K 7126-1.
Evaluation methods were performed by the following methods.
Equipment used: Gas permeability tester (manufactured by GTR Tech, model number: GTR-11AET)
Measurement method: JIS K 7126-1 (differential pressure method)
Gas to be measured: Air (21% oxygen concentration in the composition)
Measurement temperature: 25.0°C
Transmission area: ^15.2cm2

The evaluation criteria were as follows: O when the obtained oxygen permeability was 200 or less, and x when it was greater than 200. Since the lower the value of the oxygen permeability, the better the oxygen barrier property, the evaluation of ◯ indicates higher properties as a gas barrier sheet.

(Bending test)
The gas barrier sheet was folded in four and criss-crossed (folding test, performed with reference to the method adopted for moisture permeability evaluation in JP-A-2020-192737). The gas barrier property was similarly evaluated using the test piece after the bending test.

The evaluation criteria were as follows: O when the oxygen permeability obtained after the bending test was 400 or less, and x when it was greater than 400. Since the lower the value of the oxygen permeability, the better the oxygen barrier property, the evaluation of ◯ indicates higher properties as a gas barrier sheet.

(flexibility evaluation)
The flexibility was evaluated using the obtained gas barrier sheet.
A gas barrier sheet was wrapped around a cylindrical stainless steel rod (2 cm in diameter) and held for 1 hour, and surface cracks and shape changes were visually observed (performed with reference to JIS K 5600-5-1 mandrel bending test).

The evaluation criteria were as follows: ○ when no cracks or the like were observed, and x when they were observed. It is desirable that the gas barrier sheet has flexibility and does not change its shape even when a load is applied to the surface of the sheet. From this, the evaluation of ◯ indicates higher performance as a gas barrier sheet.

(Measurement of sheet total light transmittance)
The total light transmittance of the sheet was measured according to JIS K 7361-1.
In the experiment, a spectroscopic haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model number SH-7000, Ver. 2.00.02) was used for measurement.
A state of only air (a state in which nothing was set in the measurement section) was taken as a blank measurement value, and the pulp sheet for measurement was directly sandwiched between sample scissors to measure the light transmittance. The light source was D65, the field of view was 10°, and the measurement wavelength range was 380 to 780 nm.
The haze value and the total light transmittance were calculated using the numerical values obtained from the control unit of the spectroscopic haze meter (Model No. CU-II, Ver2.00.02).

(Experimental result)
FIG. 3 shows physical property values of Examples and Comparative Examples.
Sheets were produced using the samples A to I prepared in Experiment 1, and the oxygen permeability was evaluated as the gas barrier property. As a result, the sheets produced from samples A to F with basis weights in the range of 28 g/m ² to 120 g/m ² had an oxygen permeability of 200 cc/m ² ·24 hours·atm or less. In addition, the oxygen permeability was maintained even after the bending test. In other words, it was confirmed that the sheet used in the experiment exhibited excellent gas barrier properties and also had excellent flexibility.
Experimental results show that there are conventional sheets containing cellulose nanofibers to exhibit gas barrier properties, but the formation of the gas barrier layer on the surface of the sheet is likely to be lost due to bending or the like, and the gas barrier properties are likely to be lost. Since the sheet of No. 2 has flexibility similar to that of paper due to its flexibility, the surface of the sheet is less likely to bend, and is therefore considered to have excellent gas barrier properties. Moreover, since a sheet with excellent transparency can also be obtained, the degree of freedom in handling can be further improved.

(Experiment 3)
Next, for the gas barrier sheet of the present invention using the chemically modified pulp fibers prepared in Experiment 2, the results of oxygen permeability measurement using Examples 8 and 17 will be described as representatives.

(Oxygen permeability evaluation)
The obtained gas barrier sheet was used to evaluate gas barrier properties.
As a gas barrier property, oxygen permeability (cc/m ² ·24 hours · atm) was measured by a method based on JIS K 7126-1.
Evaluation methods were performed by the following methods.
Equipment used: Gas permeability tester (manufactured by GTR Tech, model number: GTR-10X)
Measurement method: JIS K 7126-1 (differential pressure method)
Gas to be measured: Oxygen gas (100% oxygen concentration in the composition)
Measurement temperature: 25.0°C
Measured humidity: 0%
Transmission area: ^15.2cm2

(Experimental result)
FIG. 4 shows the results of (Experiment 3).
As shown in FIG. 4, the oxygen permeability values after 12 hours of measurement were 4.34 for Example 8 and 198 for Example 17.
From the experimental results, it was confirmed that the sheet composed only of chemically modified pulp fibers clearly exhibits high gas barrier properties. Moreover, since this value is at the same level as a film using aluminum foil, we were able to confirm for the first time in the world that a high gas barrier property equivalent to that of an aluminum foil film could be achieved in spite of being pulp fiber.
Therefore, it was confirmed that the sheet of the present invention can serve as a substitute for a base material for various uses as a gas barrier base material derived from nature.

The gas barrier sheet of the present invention is suitable as various gas barrier substrates that require gas barrier properties.

Claims (7)

Paper-made paper containing chemically modified pulp fibers having one structure selected from the group consisting of the following general formula (1), general formula (2) and general formula (3) as at least part of the cellulose constituent units a sheet member;
The chemically modified pulp fibers are
The introduction amount of SO ₃ ^- Z when having the above general formula (1), the introduction amount of CO ₂ ^- Z when having the above general formula (2), and the introduction amount of PO ₃ ^2- when having the above general formula (3) The introduction amount of Z is 0.8 mmol/g or more and 5 mmol/g or less, respectively;
The following sheets obtained from the chemically modified pulp fibers are
A gas barrier sheet characterized by having an oxygen permeability (cc/m ² ·24 hours · atm) of 200 or less as measured by JIS K 7126-1 (differential pressure method).

(Sheet: basis weight of 10 g/m ² or more and 150 g/m ^{2 or} less, thickness of 20 μm or more and 150 μm or less, density of 0.3 g/cm ³ or more and 1.5 g/cm ³ or less)

(general formula 1))

(In the formula, R ₁ represents SO ₃ ⁻ Z or H. However, R ₁ may be the same or different, and contains at least one SO ₃ ⁻ Z. Z is hydrogen ion, metal ion , represents an onium ion or a cationic organic compound. n represents an integer of 1 or more.)

(general formula (2))

(In the formula, R ₂ represents CO ₂ ⁻ Z or H. However, R ₂ may be the same or different, and contains at least one CO ₂ ⁻ Z. Z is hydrogen ion, metal ion , represents an onium ion or a cationic organic compound. n represents an integer of 1 or more.)

(general formula (3))

(In the formula, R ₃ represents PO ₃ ^2- Z or H. However, R ₃ may be the same or different, and contains at least one PO ₃ ^2- Z. Z is a hydrogen ion, represents a metal ion, an onium ion, or a cationic organic compound, where n represents an integer of 1 or greater.)
2. The gas barrier sheet according to claim 1, wherein the content of said chemically modified pulp fibers is 50% by mass to 100% by mass. the paper sheet
3. The gas barrier sheet according to claim 1, comprising a substrate and a modified pulp layer containing said chemically modified pulp fibers. 3. The gas barrier sheet according to claim 1, wherein the modified pulp layer has a coating weight of 0.1 to 20 g/m ² . 3. The gas barrier sheet according to claim 1, wherein said paper sheet contains a resin. The paper sheet obtained from the chemically modified pulp fiber is
3. The gas barrier sheet according to claim 1, wherein the gas barrier sheet has an oxygen permeability of 400 or less after a bending test. The chemically modified pulp fibers are
The rate of change in the radial direction of the fiber is 1.3 or more and 8 or less,
The rate of change is
3. The gas barrier sheet according to claim 1, wherein the value is obtained by dividing the average swollen fiber width in a water-absorbed state by the average non-swollen fiber width in a dry state.

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